Cellular Respiration A.P. Biology.

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Presentation transcript:

Cellular Respiration A.P. Biology

powers most cellular work Energy Flows into an ecosystem as sunlight and leaves as heat Light energy ECOSYSTEM CO2 + H2O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O2 ATP powers most cellular work Heat energy Figure 9.2

Catabolic pathways yield energy by oxidizing organic fuels The breakdown of organic molecules is exergonic Fermentation Is a partial degradation of sugars that occurs without oxygen

Catabolic pathways yield energy by oxidizing organic fuels Cellular respiration Is the most prevalent and efficient catabolic pathway Consumes oxygen and organic molecules such as glucose Yields ATP

Redox Reactions: Oxidation and Reduction Catabolic pathways yield energy Due to the transfer of electrons Redox reactions Transfer electrons from one reactant to another by oxidation and reduction Oxidation A substance loses electrons, or is oxidized Reduction A substance gains electrons, or is reduced

becomes oxidized (loses electron) becomes reduced (gains electron)

Some redox reactions Do not completely exchange electrons Change the degree of electron sharing in covalent bonds CH4 H C O Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water + 2O2 CO2 Energy 2 H2O becomes oxidized becomes reduced Reactants Products Figure 9.3

Oxidation of Organic Fuel Molecules During Cellular Respiration Glucose is oxidized and oxygen is reduced C6H12O6 + 6O2 6CO2 + 6H2O + Energy becomes oxidized becomes reduced G = -686 kcal/mol

Step by step catabolism of glucose If electron transfer is not stepwise A large release of energy occurs As in the reaction of hydrogen and oxygen to form water (a) Uncontrolled reaction Free energy, G H2O Explosive release of heat and light energy Figure 9.5 A H2 + 1/2 O2

Electron transport chain (b) Cellular respiration ETC 2 H 1/2 O2 (from food via NADH) 2 H+ + 2 e– 2 H+ 2 e– H2O Controlled release of energy for synthesis of ATP ATP Electron transport chain Free energy, G (b) Cellular respiration + Figure 9.5 B The electron transport chain Passes electrons in a series of steps Uses the energy from the electron transfer to form ATP

NAD – Nicotinamide Adenine Dinucleotide (Electron Acceptor) Electrons from organic compounds Are usually 1st transferred to NAD+, a coenzyme NAD+ H O O– P CH2 HO OH N+ C NH2 N Nicotinamide (oxidized form) + 2[H] (from food) Dehydrogenase Reduction of NAD+ Oxidation of NADH 2 e– + 2 H+ 2 e– + H+ NADH Nicotinamide (reduced form) Figure 9.4 Dehydragenase – removes 2 hydrogen atoms

NADH NADH, the reduced form of NAD+ Passes the electrons to the electron transport chain Electrons are ultimately passed to a molecule of oxygen (Final electron acceptor) G = -53 kcal/mol Electron path in respiration Food  NADH  ETC  Oxygen

Cellular Respiration Respiration is a cumulative function of three metabolic stages Glycolysis The citric acid cycle (TCA or Krebbs) Oxidative phosphorylation C6H12O6 + 6O2   <---->   6 CO2 + 6 H20    + e- --->    36-38 ATP                                   DG  =  -686 Kc/mole                                263Kc  = 38%

Respiration Glycolysis The citric acid cycle Oxidative phosphorylation Breaks down glucose into two molecules of pyruvate The citric acid cycle Completes the breakdown of glucose Oxidative phosphorylation Is driven by the electron transport chain Generates ATP

Oxidative phosphorylation: electron transport and chemiosmosis Respiration Overview Figure 9.6 Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Oxidative Mitochondrion Cytosol 2 ATP 2 ATP 34 ATP

Substrate Level Phosphorylation Both glycolysis and the citric acid cycle Can generate ATP by substrate-level phosphorylation Figure 9.7 Enzyme ATP ADP Product Substrate P +

Energy investment phase Glycolysis Citric acid cycle Oxidative phosphorylation ATP 2 ATP 4 ATP used formed Glucose 2 ATP + 2 P 4 ADP + 4 2 NAD+ + 4 e- + 4 H + 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Energy investment phase Energy payoff phase 4 ATP formed – 2 ATP used 2 NAD+ + 4 e– + 4 H + Figure 9.8 Glycolysis Harvests energy by oxidizing glucose to pyruvate Glycolysis Means “splitting of sugar” Breaks down glucose into pyruvate Occurs in the cytoplasm of the cell Two major phases Energy investment phase Energy payoff phase

Energy Investment Phase

Energy Payoff Phase

Glycolysis Summary

The First Stage of Glycolysis Glucose (6C) is broken down into 2 PGAL's (3C Phosphoglyceraldehyde) This requires two ATP's

The Second Stage of Glycolysis 2 PGAL's (3C) are converted to 2 pyruvates This creates 4 ATP's and 2 NADH's The net ATP production of Glycolysis is 2 ATP's

Citric Acid Cycle a.k.a. Krebs Cycle Completes the energy-yielding oxidation of organic molecules The citric acid cycle Takes place in the matrix of the mitochondrion

Krebs's Cycle (citric acid cycle, TCA cycle) Goal: take pyruvate and put it into the Krebs's cycle, producing NADH and FADH2 Where: the mitochondria There are two steps The Conversion of Pyruvate to Acetyl CoA The Kreb's Cycle proper In the Krebs's cycle, all of Carbons, Hydrogens, and Oxygeng in pyruvate end up as CO2 and H2O The Krebs's cycle produces 2 ATP's, 8 NADH's, and 2FADH2's per glucose molecule

Fate of Pyruvate

Carboxyl (coo-) is cleaved CO2 is released

Before the citric acid cycle can begin Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysis CYTOSOL MITOCHONDRION NADH + H+ NAD+ 2 3 1 CO2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH3 O Transport protein O– Figure 9.10

Oxidative phosphorylation An overview of the citric acid cycle ATP 2 CO2 3 NAD+ 3 NADH + 3 H+ ADP + P i FAD FADH2 Citric acid cycle CoA Acetyle CoA NADH CO2 Pyruvate (from glycolysis, 2 molecules per glucose) Glycolysis Oxidative phosphorylation Figure 9.11

Figure 9.12 Acetyl CoA Oxaloacetate Malate Citrate Isocitrate Citric NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA a-Ketoglutarate Isocitrate Citric acid cycle S SH FADH2 FAD GTP GDP NAD+ ADP P i CO2 H2O + H+ C CH3 O COO– CH2 HO HC CH 1 2 3 4 5 6 7 8 Glycolysis Oxidative phosphorylation ATP Figure 9.12

The Kreb's Cycle 6 NADH's are generated 2 FADH2 is generated 2 ATP are generated 4 CO2's are released

Net Engergy Production from Aerobic Respiration Glycolysis: 2 ATP Kreb's Cycle: 2 ATP Electron Transport Phosphorylation: 32 ATP Each NADH produced in Glycolysis is worth 2 ATP (2 x 2 = 4) - the NADH is worth 3 ATP, but it costs an ATP to transport the NADH into the mitochondria, so there is a net gain of 2 ATP for each NADH produced in gylcolysis Each NADH produced in the conversion of pyruvate to acetyl COA and Kreb's Cycle is worth 3 ATP (8 x 3 = 24) Each FADH2 is worth 2 ATP (2 x 2 = 4) 4 + 24 + 4 = 32 Net Energy Production: 36 ATP

Energy Yields: Glucose: 686 kcal/mol ATP: 7.5 kcal/mol 7.5 x 36 = 270 kcal/mol for all ATP's produced 270 / 686 = 39% energy recovered from aerobic respiration

After the Krebs Cycle… During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis NADH and FADH2 Donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

The Pathway of Electron Transport In the electron transport chain Electrons from NADH and FADH2 lose energy in several steps At the end of the chain Electrons are passed to oxygen, forming water

Figure 9.13 NADH 50 40 Free energy (G) relative to O2 (kcl/mol) 30 20 H2O O2 NADH FADH2 FMN Fe•S O FAD Cyt b Cyt c1 Cyt c Cyt a Cyt a3 2 H + + 12 I II III IV Multiprotein complexes 10 20 30 40 50 Free energy (G) relative to O2 (kcl/mol) Figure 9.13

The Energy-Coupling Mechanism Chemiosmosis: The Energy-Coupling Mechanism ATP synthase Is the enzyme that actually makes ATP INTERMEMBRANE SPACE H+ P i + ADP ATP A rotor within the membrane spins clockwise when H+ flows past it down the H+ gradient. A stator anchored in the membrane holds the knob stationary. A rod (for “stalk”) extending into the knob also spins, activating catalytic sites in the knob. Three catalytic sites in the stationary knob join inorganic Phosphate to ADP to make ATP. MITOCHONDRIAL MATRIX Figure 9.14

ETC The resulting H+ gradient Electron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane space The resulting H+ gradient Stores energy Drives chemiosmosis in ATP synthase Is referred to as a proton-motive force

H+ gradient = Proton motive force Chemiosmosis Is an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular work H+ gradient = Proton motive force

Electron transport chain Oxidative phosphorylation and chemiosmosis Glycolysis ATP Inner Mitochondrial membrane H+ P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH+ FADH2 NAD+ FAD+ 2 H+ + 1/2 O2 H2O ADP + Electron transport chain Electron transport and pumping of protons (H+), which create an H+ gradient across the membrane Chemiosmosis ATP synthesis powered by the flow Of H+ back across the membrane synthase Q Oxidative phosphorylation Intermembrane space mitochondrial matrix Figure 9.15

Production by Cellular Respiration An Accounting of ATP Production by Cellular Respiration During respiration, most energy flows in this sequence Glucose to NADH to electron transport chain to proton-motive force to ATP

Figure 9.16 MITOCHONDRION CYTOSOL or Glycolysis Citric 2 acid Pyruvate Electron shuttles span membrane CYTOSOL 2 NADH 2 FADH2 6 NADH Glycolysis Glucose 2 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis MITOCHONDRION by substrate-level phosphorylation by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol Maximum per glucose: About 36 or 38 ATP + 2 ATP + about 32 or 34 ATP or Figure 9.16

Anaerobic Respiration Fermentation enables some cells to produce ATP without the use of oxygen Glycolysis Can produce ATP with or without oxygen, in aerobic or anaerobic conditions Couples with fermentation to produce ATP

Anaerobic Respiration Fermentation consists of Glycolysis plus reactions that regenerate NAD+, which can be reused by glyocolysis Alcohol fermentation Pyruvate is converted to ethanol in two steps, one of which releases CO2 Lactic acid fermentation Pyruvate is reduced directly to NADH to form lactate as a waste product

(a) Alcohol fermentation (b) Lactic acid fermentation 2 ADP + 2 P1 2 ATP Glycolysis Glucose 2 NAD+ 2 NADH 2 Pyruvate 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 Lactate (b) Lactic acid fermentation H OH CH3 C O – O O– CO2 2 Figure 9.17

Pyruvate is a key juncture in catabolism Glucose CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration Ethanol or lactate Acetyl CoA MITOCHONDRION Citric acid cycle Figure 9.18

Glycolysis Occurs in nearly all organisms Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

Figure 9.19 Glucose NH3 Pyruvate Amino acids Sugars Glycerol Fatty Glycolysis Glucose Glyceraldehyde-3- P Pyruvate Acetyl CoA NH3 Citric acid cycle Oxidative phosphorylation Fats Proteins Carbohydrates Figure 9.19

Fructose-1,6-bisphosphate Cellular respiration Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle Glucose Glycolysis Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate Inhibits Pyruvate ATP Acetyl CoA Citric acid cycle Citrate Oxidative phosphorylation Stimulates AMP + – Figure 9.20